[ARC5] dB Power Apples and dB Voltage Oranges, was Re: Selectivity Ratings...

Tue Oct 29 18:06:08 EDT 2013

dBm is a fairly recent change brought about by modern test equipment but 
that power reading is displayed on the signal generator and not at any stage 
thru the radio.

Carl

----- Original Message ----- 
From: "jmfranke" <jmfranke at cox.net>
To: "K5MYJ" <macklinbob at gmail.com>; <n4fs at eozinc.com>; <aj1g at sbcglobal.net>; 
<k2gkk at hotmail.com>; <vk2bcu at operamail.com>; "Jay Coward" 
<jcoward5452 at aol.com>
Cc: <arc5 at mailman.qth.net>
Sent: Tuesday, October 29, 2013 5:20 PM
Subject: Re: [ARC5] dB Power Apples and dB Voltage Oranges,was Re: 
Selectivity Ratings...

> It is measured in either microvolts or power. MDS is typically given in 
> dBM as in -131 dBm or -161 dBm-1.
>
> John  WA4WDL
>
> --------------------------------------------------
> From: "K5MYJ" <macklinbob at gmail.com>
> Sent: Tuesday, October 29, 2013 5:01 PM
> To: <n4fs at eozinc.com>; <aj1g at sbcglobal.net>; <k2gkk at hotmail.com>; 
> <vk2bcu at operamail.com>; "Jay Coward" <jcoward5452 at aol.com>
> Cc: <arc5 at mailman.qth.net>
> Subject: Re: [ARC5] dB Power Apples and dB Voltage Oranges,was Re: 
> Selectivity Ratings...
>
>> Does an S-Meter reflect POWER or VOLTAGE?
>>
>> Receiver sensitivity is measured in microvolts! NOT POWER!
>>
>> Bob Macklin
>> K5MYJ
>> Seattle, Wa.
>> "Real Radios Glow In The Dark"
>> ----- Original Message ----- 
>> From: "Jay Coward" <jcoward5452 at aol.com>
>> To: <n4fs at eozinc.com>; <aj1g at sbcglobal.net>; <k2gkk at hotmail.com>; 
>> <vk2bcu at operamail.com>
>> Cc: <arc5 at mailman.qth.net>
>> Sent: Tuesday, October 29, 2013 1:52 PM
>> Subject: Re: [ARC5] dB Power Apples and dB Voltage Oranges, was Re: 
>> Selectivity Ratings...
>>
>>
>>>
>>> In tech school we learned it like this: For a decernable increase in 
>>> received signal, you had to increase transmitter power by four times. I 
>>> think there were problems on the FCC 2nd class test like this.
>>> Jay
>>>
>>>
>>>
>>> -----Original Message-----
>>> From: Mike Feher <n4fs at eozinc.com>
>>> To: 'Christopher Bowne' <aj1g at sbcglobal.net>; 'D C _Mac_ Macdonald' 
>>> <k2gkk at hotmail.com>; 'Leslie Smith' <vk2bcu at operamail.com>
>>> Cc: 'ARC-5 List' <arc5 at mailman.qth.net>
>>> Sent: Tue, Oct 29, 2013 1:11 pm
>>> Subject: Re: [ARC5] dB Power Apples and dB Voltage Oranges, was Re: 
>>> Selectivity Ratings...
>>>
>>>
>>> Chris -
>>> Without going into the details, I'll let you do it, but, you should 
>>> re-think
>>> his as your conclusion is in error. 73 - Mike
>>> Mike B. Feher, N4FS
>>> 9 Arnold Blvd.
>>> owell, NJ, 07731
>>> 32-886-5960
>>>
>>> ----Original Message-----
>>> rom: arc5-bounces at mailman.qth.net [mailto:arc5-bounces at mailman.qth.net] 
>>> On
>>> ehalf Of Christopher Bowne
>>> ent: Tuesday, October 29, 2013 1:19 PM
>>> o: D C _Mac_ Macdonald; Leslie Smith
>>> c: ARC-5 List
>>> ubject: [ARC5] dB Power Apples and dB Voltage Oranges, was Re: 
>>> Selectivity
>>> atings...
>>> When you are measuring the selectivity of a circuit, you typically are
>>> ooking at a voltage measurement.  dB change relative to a reference 
>>> voltage
>>> ollows the equation:
>>> dBx = 20 X log(vx/vref)
>>> so a doubling of a measured voltage relative to a reference voltage to a
>>> esults in a 6 dB increase.
>>> Power changes follow the equation dBx = 10 X log (px/pref)
>>> so a doubling of power will result in a 3 dB increase.
>>> So if you are running 100 watts output to you antenna, and then put your 
>>> 1KW
>>> utput linear amplifier on service, you power output will increase by 10 
>>> dB.
>>> The S-meter reading  at a receiving station, however, assuming that it 
>>> has a
>>> dB per S unit calibration that is measuring a voltage, will show an
>>> ncrease of 20 dB, or over 2 S units.  Same result for a field strength
>>> eter.
>>> I think I just convinced myself that, as far as the effects observed on 
>>> a
>>> eceiving station's S meter are concerned, adding 10 dB of power gain 
>>> with
>>> n amplifieris twice as effective as adding 10 dB of antenna pattern 
>>> gain,
>>> ince  unless I am missing something, antenna gain measurements are made
>>> omparing differences in received voltages of a field strength meter.
>>> It all goes back to the power equation Power in Watts = Voltage
>>> quared/Resistance.
>>>
>>>
>>>
>>>
>>> _______________________________
>>> From: D C _Mac_ Macdonald <k2gkk at hotmail.com>
>>> o: Leslie Smith <vk2bcu at operamail.com>
>>> c: ARC-5 List <arc5 at mailman.qth.net>
>>> ent: Tuesday, October 29, 2013 11:56 AM
>>> ubject: Re: [ARC5] Selectivity ratings of ARC-5 receivers.
>>>
>>> You have to remember that if you double the voltage applied to a fixed
>>> esistance/impedance you will also get double the current giving FOUR 
>>> times
>>> he power (6 dB)!
>>>
>>> 3 - Mac, K2GKK/5 in OKC
>>>
>>> ent from my iPad
>>>> On Oct 29, 2013, at 0:08, "Leslie Smith" <vk2bcu at operamail.com> wrote:
>>>
>>>  Hello Ken,
>>>  I'll be a goose and make a public fool of myself.
>>>  Dad always said, "Remember son, there's no bigger fool than a public
>>>  fool."
>>>  The units of measurement 2x and 1000x are voltage (measured with a
>>>  volt-meter or CRO or similar meter)
>>>
>>>  I understand 1 "S" unit equals 6 dB - and in my view this is too
>>>  small.
>>>
>>>  "My thinking (your thinking) is that in order to achieve a 3bD
>>>  increase in signal level at the receiver the transmitter [output
>>>  power] must be doubled"
>>>  That's correct, assuming your unit of measurement is power.
>>>  But at the receiver your unit of measurement is voltage.
>>>  dB = 20log(E2/E1)  so 20log(1000/1) is 20 * 3 = 60
>>>  For a 50% increase in voltage level 20 * log (2/1) = 20 * 0.3010 =
>>>  6dB.
>>>
>>>  Sorry to be long winded
>>>
>>>
>>>  73 de Les Smith
>>>  vk2bcu at operamail.com
>>>
>>>
>>>> On Tue, Oct 29, 2013, at 14:31, Kenneth G. Gordon wrote:
>>>> Reading the ARC-5 maintenance manual, I see that the selectivity for,
>>>> say, the R-26 (3 - 6 MHz) receiver is listed at 7.3 Kc at 2X, and 26
>>>> Kc at 1000X.
>>>>
>>>> Now 1000X is 60 db, but isn't 2X 3db and not 6db?
>>>>
>>>> Color me confused at this point.
>>>>
>>>> My thinking is that in order to achieve a 3db increase in signal
>>>> level at the receiver, the transmitter must be doubled in output
>>>> power, given identical conditions.
>>>>
>>>> Or am I all wet here?
>>>>
>>>> Ken W7EKB
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